Coating composition and method of forming coating film

ABSTRACT

The present invention provides a thermosetting and photocurable coating composition obtained by incorporating a copolymer of a maleimide group-containing monomer with other monomer(s) or a specific maleimide compound into a composition comprising a hydroxyl-containing resin and a curing agent and optionally containing an unsaturated compound; and a method of forming a coating film using the coating composition.

TECHNICAL FIELD

The present invention relates to a coating composition and a method offorming a coating film.

BACKGROUND ART

For the formation of a coating film on the bodies of vehicles such asautomobiles, motorcycles, and the like, one widely used method comprisesapplying a thermosetting coating composition that contains a resinhaving thermosetting functional groups, such as a hydroxyl-containingacrylic resin, and a curing agent, such as a melamine resin, to avehicle body to be coated, and thereafter curing the applied coatingcomposition by heating. This method can form a coating film havingexcellent film properties in terms of gasoline resistance, adhesion,etc.

In recent years, it has been desired to reduce energy consumption andincrease productivity in the above-mentioned coating film formationmethod. For example, the heat-curing step on an automobile body coatingline is usually conducted at about 140° C. for about 40 minutes; whenthe conveyor runs at a speed of 3 m/min, the step requires a space forthe drying furnace line about 120 m in length. Therefore, in order tosave space and energy, shortening of the heating time in the heat-curingstep is demanded. Moreover, reduction of the heating time is preferableso as to decrease CO₂, soot, etc., which cause environmental problems.

In addition, in view of better appearance, the coating film formed on anautomobile body is now increasingly required to have improved resistanceto marring by car washes, scratching around keyholes, etc. It has thusbecome important to develop a coating composition that can form acoating film having excellent resistance to marring or scratching on anautomobile body or the like.

Use of coating compositions that are curable by active energy rays suchas ultraviolet rays is effective for reducing or omitting heating steps.For example, Japanese Unexamined Patent Publications No. 1999-124403 andNo. 1999-124404 disclose an active energy ray-curable compositioncomprising a maleimide derivative that can be cured under ultravioletirradiation. However, although coating with such a composition canshorten the time to cure a coating film or can reduce the size ofcoating facilities, the curing of the coating film is insufficient, sothat it is difficult to obtain a coating film having excellentproperties in mar resistance, scratch resistance, gasoline resistance,adhesion, etc.

Japanese Unexamined Patent Publications No. 2001-220536 and No.2002-320910 disclose an active energy ray-curable coating compositioncomprising an acrylic resin wherein the acrylic resin is a copolymer ofa (meth)acrylic acid alkyl ester, a (meth)acrylic acid hydroxyalkylester, and a monomer having an unsaturated double bond and a maleimidegroup; and a coating method using this coating composition. However,although such a coating composition or coating method can shorten thetime to cure a coating film or can reduce the size of coatingfacilities, the curing of the coating film is insufficient. As a result,no coating films can be obtained that are suitable for the bodies ofautomobiles, etc., having excellent properties in mar resistance,scratch resistance, gasoline resistance, adhesion, etc.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a coating compositionthat enables shortening of the heating time for forming a cured coatingfilm, thereby contributing to saving space and energy as well asreducing CO₂ and other agents of environmental damage; and that forms acoating film having excellent properties in terms of mar resistance,scratch resistance, gasoline resistance, adhesion, etc.

Another object of the invention is to provide a method of forming acoating film using the above coating composition.

Further objects and features of the invention will be apparent from thefollowing description.

In order to achieve the above objects, the present inventors conductedextensive research. As a result, the inventors found that the aboveobjects can be achieved by a thermosetting and photocurable coatingcomposition obtained by incorporating a copolymer of a maleimidegroup-containing monomer with other monomer(s) or a specific maleimidecompound into a composition comprising a hydroxyl-containing resin and acuring agent and optionally containing an unsaturated compound. Based onsuch novel findings, the inventors accomplished the present invention.

The present invention provides the following coating compositions andmethods of forming a coating film using such coating compositions:

Item 1: A thermosetting and photocurable coating composition comprising:

(A) a hydroxyl-containing resin;(B) a maleimide group-containing copolymer obtained by radicalcopolymerization of a maleimide group-containing monomer (a) with atleast one other monomer;(C) a curing agent; and(D) at least one unsaturated compound selected from the group consistingof radical polymerizable unsaturated monomers, radical polymerizableunsaturated group-containing resins, and radical polymerizableunsaturated group- and thermosetting functional group-containing resins.

Item 2: A coating composition according to item 1, wherein thehydroxyl-containing resin (A) is a hydroxyl-containing polyester resinproduced by esterifying a polybasic acid (b) with a polyhydric alcohol(c), wherein an alicyclic polybasic acid (b1) and/or an alicyclicpolyhydric alcohol (c1) are included in a proportion of 20% or more byweight based on the total weight of polybasic acid (b) and polyhydricalcohol (c).

Item 3: A coating composition according to item 1, wherein the maleimidegroup-containing monomer (a) used for obtaining the copolymer (B) is atetrahydrophthalmaleimide (meth)acrylate represented by formula (1):

wherein R represents hydrogen atom or methyl group.

Item 4: A coating composition according to item 1, wherein the curingagent (C) is a polyisocyanate compound.

Item 5: A coating composition according to item 1, wherein the curingagent (C) is a combination of a polyisocyanate compound and a melamineresin.

Item 6: A coating composition according to item 1, comprising 20% to 60%by weight of hydroxyl-containing resin (A), 10% to 45% by weight ofcopolymer (B), and 5% to 50% by weight of curing agent (C) based on thetotal weight of hydroxyl-containing resin (A), copolymer (B), and curingagent (C); and comprising 1 to 50 parts by weight of unsaturatedcompound (D) per 100 parts by weight of the total of hydroxyl-containingresin (A), copolymer (B), and curing agent (C).

Item 7: A coating composition according to item 1, further comprising0.1 to 20 parts by weight of photopolymerization initiator (F) per 100parts by weight of the total of hydroxyl-containing resin (A), copolymer(B), and curing agent (C).

Item 8: A coating composition according to item 1, wherein the coatingcomposition is a clear coating composition for automobile bodies orautomobile body parts.

Item 9: A thermosetting and photocurable coating composition comprising:

(A) a hydroxyl-containing resin;(C) a curing agent; and(E) a maleimide compound represented by formula (2):

wherein m is an integer from 1 to 6, n is an integer from 1 to 17, andthe maleimide compound (E) has a number average molecular weight of2,000 or less.

Item 10: A coating composition according to item 9, wherein thehydroxyl-containing resin (A) is a hydroxyl-containing polyester resinproduced by esterifying a polybasic acid (b) with a polyhydric alcohol(c), wherein an alicyclic polybasic acid (b1) and/or an alicyclicpolyhydric alcohol (c1) are included in a proportion of 20% or more byweight based on the total weight of polybasic acid (b) and polyhydricalcohol (c).

Item 11: A coating composition according to item 9, wherein the curingagent (C) is a polyisocyanate compound.

Item 12: A coating composition according to item 9, wherein the curingagent (C) is a combination of a polyisocyanate compound and a melamineresin.

Item 13: A coating composition according to item 9, comprising 60% to90% by weight of hydroxyl-containing resin (A) and 10% to 40% by weightof curing agent (C) based on the total weight of hydroxyl-containingresin (A) and curing agent (C); and comprising 1 to 50 parts by weightof maleimide compound (E) per 100 parts by weight of the total ofhydroxyl-containing resin (A) and curing agent (C).

Item 14: A coating composition according to item 9, further comprising,per 100 parts by weight of the total of hydroxyl-containing resin (A)and curing agent (C), 1 to 50 parts by weight of at least oneunsaturated compound (D) selected from the group consisting of radicalpolymerizable unsaturated monomers, radical polymerizable unsaturatedgroup-containing resins, and radical polymerizable unsaturated group-and thermosetting functional group-containing resins.

Item 15: A coating composition according to item 9, further comprising0.1 to 20 parts by weight of photopolymerization initiator (F) per 100parts by weight of the total of hydroxyl-containing resin (A) and curingagent (C).

Item 16: A coating composition according to item 9, wherein the coatingcomposition is a clear coating composition for automobile bodies orautomobile body parts.

Item 17: A thermosetting and photocurable coating compositioncomprising:

(A) a hydroxyl-containing resin;(B) a maleimide group-containing copolymer obtained by radicalcopolymerization of a maleimide group-containing monomer (a) with atleast one other monomer;(C) a curing agent; and(E) a maleimide compound represented by formula (2):

wherein m is an integer from 1 to 6, n is an integer from 1 to 17, andthe maleimide compound (E) has a number average molecular weight of2,000 or less.

Item 18: A coating composition according to item 17, wherein thehydroxyl-containing resin (A) is a hydroxyl-containing polyester resinproduced by esterifying a polybasic acid (b) with a polyhydric alcohol(c), wherein an alicyclic polybasic acid (b1) and/or an alicyclicpolyhydric alcohol (c1) are included in a proportion of 20% or more byweight based on the total weight of polybasic acid (b) and polyhydricalcohol (c).

Item 19: A coating composition according to item 17, wherein themaleimide group-containing monomer (a) of the copolymer (B) is atetrahydrophthalmaleimide (meth)acrylate represented by formula (1):

wherein R represents hydrogen atom or methyl group.

Item 20: A coating composition according to item 17, wherein the curingagent (C) is a polyisocyanate compound.

Item 21: A coating composition according to item 17, wherein the curingagent (C) is a combination of a polyisocyanate compound and a melamineresin.

Item 22: A coating composition according to item 17, comprising 20% to60% by weight of hydroxyl-containing resin (A), 10% to 45% by weight ofcopolymer (B), and 5% to 50% by weight of curing agent (C) based on thetotal weight of hydroxyl-containing resin (A), copolymer (B), and curingagent (C); and comprising 1 to 50 parts by weight of maleimide compound(E) per 100 parts by weight of the total of hydroxyl-containing resin(A), copolymer (B), and curing agent (C).

Item 23: A coating composition according to item 17, further comprising,per 100 parts by weight of the total of hydroxyl-containing resin (A),copolymer (B), and curing agent (C), 1 to 50 parts by weight of at leastone unsaturated compound (D) selected from the group consisting ofradical polymerizable unsaturated monomers, radical polymerizableunsaturated group-containing resins, and radical polymerizableunsaturated group- and thermosetting functional group-containing resins.

Item 24: A coating composition according to item 17, further comprising0.1 to 20 parts by weight of photopolymerization initiator (F) per 100parts by weight of the total of hydroxyl-containing resin (A), copolymer(B), and curing agent (C).

Item 25: A coating composition according to item 17, wherein the coatingcomposition is a clear coating composition for automobile bodies orautomobile body parts.

Item 26: A method of forming a coating film comprising forming one ortwo colored base coats and one or two clear coats on a substrate to becoated to form a multilayer coating film, the top clear coat beingformed from the coating composition of item 1.

Item 27: A method of forming a coating film according to item 26,wherein a colored base coat and a top clear coat are formed on thesubstrate to form a multilayer coating film.

Item 28: A method of forming a coating film according to item 26,wherein a colored base coat, a clear coat, and a top clear coat areformed on the substrate to form a multilayer coating film.

Item 29: A method of forming a coating film according to item 26,wherein a first colored base coat, a second colored base coat, and a topclear coat are formed on the substrate to form a multilayer coatingfilm.

Item 30: A method of forming a coating film according to item 26,wherein the substrate is an automobile body or an automobile body part.

Item 31: An automobile body or an automobile body part having a coatingfilm formed thereon by the method of forming a coating film according toitem 30.

Item 32: A method of forming a coating film comprising forming one ortwo colored base coats and one or two clear coats on a substrate to becoated to form a multilayer coating film, the top clear coat beingformed from the coating composition of item 9.

Item 33: A method of forming a coating film according to item 32,wherein a colored base coat and a top clear coat are formed on thesubstrate to form a multilayer coating film.

Item 34: A method of forming a coating film according to item 32,wherein a colored base coat, a clear coat, and a top clear coat areformed on the substrate to form a multilayer coating film.

Item 35: A method of forming a coating film according to item 32,wherein a first colored base coat, a second colored base coat, and a topclear coat are formed on the substrate to form a multilayer coatingfilm.

Item 36: A method of forming a coating film according to item 32,wherein the substrate is an automobile body or an automobile body part.

Item 37: An automobile body or an automobile body part having a coatingfilm formed thereon by the method of forming a coating film according toitem 36.

Item 38: A method of forming a coating film comprising forming one ortwo colored base coats and one or two clear coats on a substrate to becoated to form a multilayer coating film, the top clear coat beingformed from the coating composition of item 17.

Item 39: A method of forming a coating film according to item 38,wherein a colored base coat and a top clear coat are formed on thesubstrate to form a multilayer coating film.

Item 40: A method of forming a coating film according to item 38,wherein a colored base coat, a clear coat, and a top clear coat areformed on the substrate to form a multilayer coating film.

Item 41: A method of forming a coating film according to item 38,wherein a first colored base coat, a second colored base coat, and a topclear coat are formed on the substrate to form a multilayer coatingfilm.

Item 42: A method of forming a coating film according to item 38,wherein the substrate is an automobile body or an automobile body part.

Item 43: An automobile body or an automobile body part having a coatingfilm formed thereon by the method of forming a coating film according toitem 42.

Thermosetting and Photocurable Coating Composition

The thermosetting and photocurable coating composition of the presentinvention can be obtained by incorporating (B) a copolymer of amaleimide group-containing monomer (a) with other monomer(s) or (E) aspecific maleimide compound into a composition comprising (A) ahydroxyl-containing resin and (C) a curing agent and optionallycontaining (D) an unsaturated compound.

The coating composition of the present invention can be classified intothermosetting and photocurable coating composition (I), thermosettingand photocurable coating composition (II), and thermosetting andphotocurable coating composition (III) as follows:

Thermosetting and Photocurable Coating Composition (I)

Thermosetting and photocurable coating composition (I) comprises: (A) ahydroxyl-containing resin; (B) a maleimide group-containing copolymerobtained by radical copolymerization of a maleimide group-containingmonomer (a) with at least one other monomer; (C) a curing agent; and (D)at least one unsaturated compound selected from the group consisting ofradical polymerizable unsaturated monomers, radical polymerizableunsaturated group-containing resins, and radical polymerizableunsaturated group- and thermosetting functional group-containing resins.

Hydroxyl-Containing Resin (A)

Hydroxyl-containing resin (A) contains two or more hydroxyl groups permolecule. The resin (A) may optionally contain carboxyl group(s).Examples of such resins (A) include hydroxyl-containing polyesterresins, hydroxyl-containing acrylic resins, etc.

Hydroxyl-containing polyester resins are produced by esterifyingpolybasic acid(s) (b) and polyhydric alcohol(s) (c) by standard methods.Such esterification may be carried out by direct esterification methodsand transesterification methods.

Examples of polybasic acids (b) include dibasic acids such as phthalicanhydride, isophthalic acid, terephthalic acid,cyclohexane-1,3-dicarboxylic acid, cyclohexane-1,4-dicarboxylic acid,hexahydrophthalic acid, hexahydroisophthalic acid, hexahydroterephthalicacid, hexahydrotrimellitic acid, tetrahydrophthalic acid, methylhexahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalicanhydride, succinic acid, fumaric acid, adipic acid, sebacic acid,maleic anhydride, etc.; lower alkyl esters of dibasic acids; tribasic orhigher polybasic acids such as trimellitic anhydride, methylcyclohexenetricarboxylic acid, pyromellitic anhydride, etc.; and so on.

Of the above polybasic acids (b), alicyclic polybasic acids (b1) arepreferable. It is preferable to use alicyclic polybasic acids (b1)having one or two 4- to 6-membered rings or like alicyclic structuresand two or more carboxyl groups per molecule. Examples of alicyclicpolybasic acids (b1) include cyclohexane-1,3-dicarboxylic acid,cyclohexane-1,4-dicarboxylic acid, hexahydrophthalic acid,hexahydroisophthalic acid, hexahydroterephthalic acid,hexahydrotrimellitic acid, tetrahydrophthalic acid, methylhexahydrophthalic acid; anhydrides of these acids; etc. Of suchalicyclic polybasic acids, cyclohexane-1,4-dicarboxylic acid isespecially preferable.

One or more polybasic acids selected from the above dibasic acids andlower alkyl esters thereof are mainly used as the polybasic acid (b),with tribasic or higher polybasic acids being optionally used. Ifnecessary, the above polybasic acids may be used in combination withmonobasic acids such as benzoic acid, crotonic acid, p-t-butylbenzoicacid, etc. for molecular weight adjustment, etc. Oil fatty acids such ascoconut oil fatty acid, dehydrated castor oil fatty acid, etc. may alsobe used.

Usable polyhydric alcohols (c) include dihydric alcohols, which have twohydroxyl groups per molecule, and polyhydric alcohols having three ormore hydroxyl groups per molecule.

Examples of dihydric alcohols include glycols such as ethylene glycol,propylene glycol, diethylene glycol, trimethylene glycol, tetraethyleneglycol, triethylene glycol, dipropylene glycol, 1,4-butanediol,1,3-butanediol, 2,3-butanediol, 1,2-butanediol, 3-methyl-1,2-butanediol,1,2-pentanediol, 1,5-pentanediol, 1,4-pentanediol, 2,4-pentanediol,2,3-dimethyltrimethylene glycol, tetramethylene glycol,3-methyl-4,5-pentanediol, 2,2,4-trimethyl-1,3-pentanediol,1,6-hexanediol, 1,5-hexanediol, 1,4-hexanediol, 2,5-hexanediol,neopentyl glycol, hydroxypivalic acid neopentyl glycol ester, etc.;polylactone diols obtained by the addition of lactones such asε-caprolactone or the like to such glycols; polyester diols such asbis(hydroxyethyl) terephthalate, etc.; alicyclic dihydric alcohols suchas cyclohexane-1,4-dimethylol, hydrogenated bisphenol-A, spiroglycol,dihydroxymethyltricyclodecane, etc.; and so on.

Examples of polyhydric alcohols having three or more hydroxyl groups permolecule include glycerin, trimethylolpropane, trimethylolethane,diglycerin, triglycerin, 1,2,6-hexanetriol, pentaerythritol,dipentaerythritol, sorbitol, mannitol, etc.

Of the above polyhydric alcohols (c), alicyclic polyhydric alcohols (c1)are preferable. It is preferable to use alicyclic polyhydric alcoholshaving one or two 4- to 6-membered rings or like alicyclic structuresand two or more hydroxyl groups per molecule. Examples of alicyclicpolyhydric alcohols (c1) include cyclohexane-1,4-dimethylol,hydrogenated bisphenol-A, spiroglycol, dihydroxymethyltricyclodecane,etc. Of such alicyclic polyhydric alcohols, cyclohexane-1,4-dimethylolis especially preferable.

In the preparation of a polyester resin, the polybasic acid(s) (b) andthe polyhydric alcohol(s) (c) include at least one member selected fromthe group consisting of alicyclic polybasic acids (b1) and alicyclicpolyhydric alcohols (c1) in a proportion of about 20% or more by weight,preferably about 30% to about 70% by weight, and more preferably about40% to about 65% by weight, based on the total solids weight ofpolybasic acid(s) (b) and polyhydric alcohol(s) (c). The use of thepolyester resin thus produced contributes to further improvement ofcoating film properties in terms of mar resistance (including resistanceto marring by car washes), scratch resistance, etc.

The hydroxyl-containing polyester resin preferably has a weight averagemolecular weight of about 500 to about 500,000, more preferably about1,000 to about 100,000, and even more preferably about 2,000 to about50,000. The hydroxyl-containing polyester resin preferably has ahydroxyl value of about 20 to about 800 mg KOH/g, and more preferablyabout 80 to about 200 mg KOH/g. The hydroxyl-containing polyester resinpreferably has an acid value of about 4 to about 200 mg KOH/g, and morepreferably about 4 to about 100 mg KOH/g.

Hydroxyl-containing acrylic resins are copolymer resins obtained byradical copolymerization of a hydroxyl-containing acrylic monomer withother monomer(s).

A hydroxyl-containing monomer is a compound having one or more hydroxylgroups and one or more polymerizable unsaturated bonds per molecule.Examples of such monomers include monoesterification products of glycolshaving 2 to 20 carbon atoms with (meth)acrylic acid, such ashydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl(meth)acrylate, etc.

Examples of monomers other than hydroxyl-containing monomers includeC₁₋₂₂ alkyl esters of (meth)acrylic acid, C₂₋₁₈ alkoxyalkyl esters of(meth)acrylic acid, amino acrylic monomers, acrylamide monomers,epoxy-containing monomers, carboxyl-containing monomers, monomers havingboth isocyanate group(s) and polymerizable unsaturated group(s) in thesame molecule, etc.

Examples of C₁₋₂₂ alkyl esters of (meth)acrylic acid include methyl(meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl(meth)acrylate, hexyl (meth)acrylate, octyl (meth)acrylate, lauryl(meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate,isobornyl (meth)acrylate, etc.

Examples of C₂₋₁₈ alkoxyalkyl esters of (meth)acrylic acid includemethoxybutyl (meth)acrylate, methoxyethyl (meth)acrylate, etc.

Examples of amino acrylic monomers include N,N-dimethylaminoethyl(meth)acrylate, N,N-diethylaminoethyl (meth)acrylate,N-t-butylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl(meth)acrylate, etc.

Examples of acrylamide monomers include acrylamide, methacrylamide,N-methylacrylamide, N-methylmethacrylamide, N-ethylacrylamide,N-ethylmethacrylamide, N-butylacrylamide, N-butylmethacrylamide,N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, etc.

Examples of epoxy-containing monomers include glycidyl acrylate,glycidyl methacrylates, etc.

Examples of carboxyl-containing monomers include acrylic acid,methacrylic acid, maleic acid, itaconic acid, fumaric acid, andmesaconic acid; anhydrides and half-esterification products of these;etc.

Examples of monomers having both isocyanate group(s) and polymerizableunsaturated group(s) in the same molecule include isocyanate ethylmethacrylate, m-isopropenyl-α,α′-dimethylbenzyl isocyanate (commonlyreferred to as m-TMI), etc.

Further examples of monomers other than hydroxyl-containing monomersinclude styrene, α-methylstyrene, vinyltoluene, acrylonitrile, vinylacetate, vinyl chloride, “Veova 9” and “Veova 10” (trade names; productsof Japan Epoxy Resins Co., Ltd.; unsaturated vinylation products ofversatic acid), etc.

Such monomers other than hydroxyl-containing monomers may be used singlyor in combination of two or more.

The hydroxyl-containing acrylic resin preferably has a number averagemolecular weight of about 1,000 to about 50,000, and more preferablyabout 2,000 to about 20,000. The hydroxyl-containing acrylic resinpreferably has a hydroxyl value of about 20 to about 200 mg KOH/g, andmore preferably about 50 to about 150 mg KOH/g.

Maleimide Group-Containing Copolymer (B)

The copolymer (B) is a maleimide group-containing copolymer obtained byradical copolymerization of a maleimide group-containing monomer (a)with one or more other monomers.

The maleimide group-containing monomer (a) preferably has apolymerizable unsaturated group and a maleimide group represented byformula (3):

wherein R₁ and R₂ each independently represent hydrogen or an alkylgroup having 4 or less carbon atoms, or R₁ and R₂ may be linked togetherto form a 5- or 6-membered hydrocarbon ring.

Examples of alkyl groups having 4 or less carbon atoms represented by R₁and R₂ include methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl,tert-butyl, etc. Examples of the 5- or 6-membered hydrocarbon ringswherein R₁ and R₂ are linked together include cyclopentyl rings,cyclohexyl rings, etc.

A particularly preferable maleimide group-containing monomer (a) is themaleimide (meth)acrylate represented by formula (4):

wherein R₁ and R₂ are as defined above; R₃ represents an optionallybranched alkylene group or optionally branched alkenylene group; R₄represents hydrogen atom or methyl group; and n is an integer from 1 to6.

Preferable examples of the optionally branched alkylene grouprepresented by R₃ include lower alkylene groups having 2 to 4 carbonatoms, such as ethylene, trimethylene, propylene, etc. Preferableexamples of the optionally branched alkenylene group represented by R₃include lower alkenylene groups having 2 to 4 carbon atoms, such asvinylene, propenylene, vinylidene, etc.

Of the monomers represented by formula (4), thetetrahydrophthalmaleimide (meth)acrylate represented by formula (1):

wherein R represents hydrogen atom or methyl group, is especiallypreferable for improving the mar resistance (including resistance tomarring by car washes), scratch resistance, gasoline resistance,adhesion, and other coating film properties of a composition using theresulting copolymer (B).

Examples of monomers other than maleimide group-containing monomer (a)include C₁₋₂₂ alkyl esters of (meth)acrylic acid, C₂₋₁₈ alkoxyalkylesters of (meth)acrylic acid, amino acrylic monomers, acrylamidemonomers, epoxy-containing monomers, carboxyl-containing monomers,monomers having both isocyanate group(s) and polymerizable unsaturatedgroup(s) in the same molecule, etc. Specific examples of such monomersare as mentioned above as examples of monomers other thanhydroxyl-containing monomers in the hydroxyl-containing acrylic resin.

Examples of monomers other than maleimide group-containing monomer (a)also include hydroxyl-containing monomers having one or more hydroxylgroups and one or more polymerizable unsaturated bonds per molecule,such as monoesterification products of glycols having 2 to 20 carbonatoms with (meth)acrylic acid. Specific examples thereof arehydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl(meth)acrylate, etc.

Further examples of monomers other than maleimide group-containingmonomer (a) include styrene, α-methylstyrene, vinyltoluene,acrylonitrile, vinyl acetate, vinyl chloride, “Veova 9” and “Veova 10”(trade names; products of Japan Epoxy Resins Co., Ltd.; unsaturatedvinylation products of versatic acid), etc.

Such monomers other than maleimide group-containing monomer (a) may beused singly or in combination of two or more.

Furthermore, maleimide group-containing copolymer (B) may be a copolymerhaving unsaturated group(s) introduced into the copolymer obtained byradical copolymerization of a maleimide group-containing monomer (a)with other monomer(s).

Methods for the introduction of such unsaturated groups are, forexample, those described in (1) to (4) below. The above-mentionedmonomers may be used in these methods.

(1) A method wherein a copolymer is obtained by radical copolymerizationof a maleimide group-containing monomer (a) with other monomer(s)including hydroxyl-containing monomer(s), and thereafter a monomerhaving both isocyanate group(s) and polymerizable unsaturated group(s)in the same molecule is added to all or some of the hydroxyl groups ofthe copolymer by urethanation reaction.

(2) A method wherein a copolymer is obtained by radical copolymerizationof a monomer having both isocyanate group(s) and polymerizableunsaturated group(s) in the same molecule, a maleimide group-containingmonomer (a), and other monomer(s); and thereafter a hydroxyl-containingmonomer is added to all or some of the isocyanate groups of thecopolymer by urethanation reaction.

(3) A method wherein a copolymer is obtained by radical copolymerizationof a maleimide group-containing monomer (a) with other monomer(s)including epoxy-containing monomer(s), and thereafter acarboxyl-containing monomer is added to all or some of the epoxy groupsof the copolymer by acid-epoxy reaction.

(4) A method wherein a copolymer is obtained by radical copolymerizationof a maleimide group-containing monomer (a) with other monomer(s)including carboxyl-containing monomer(s), and thereafter anepoxy-containing monomer is added to all or some of the carboxyl groupsof the copolymer by acid-epoxy reaction.

A copolymer (B) can be synthesized by radical copolymerization of amaleimide group-containing monomer (a) with other monomer(s) in thepresence of a radical polymerization initiator, and optionallyintroducing unsaturated bond(s) into the copolymer. Polymerization canbe carried out by methods such as block polymerization, suspensionpolymerization or emulsion polymerization in an aqueous medium, solutionpolymerization in an organic solvent, etc.

In the synthesis of a copolymer (B), the proportions of the maleimidegroup-containing monomer (a) and the other monomer(s) are preferably inthe range of about 1% to about 50% by weight of the maleimidegroup-containing monomer (a) and about 99% to about 50% by weight of theother monomer(s), based on the total monomer solids weight.

Examples of radical polymerization initiators include peroxides such asdiisopropyl peroxydicarbonate, tert-butyl peroxypivalate, benzoylperoxide, lauroyl peroxide, etc.; azo compounds such asazobisisobutyronitrile, azobisisovaleronitrile, etc.; inorganicperoxides such as ammonium persulfate, potassium persulfate, etc.; andso on. The amount of radical polymerization initiator is preferablyabout 0.1% to about 10% by weight relative to the total monomer weight.

The copolymer (B) preferably has a number average molecular weight ofabout 1,000 to about 1,000,000. When used as an organic solution-solublepolymer for coating composition, the copolymer (B) more preferably has anumber average molecular weight of about 3,000 to about 30,000. Whenemulsified/suspended in an aqueous medium for use, the copolymer (B)more preferably has a number average molecular weight of about 10,000 toabout 500,000.

Curing Agent (C)

The curing agent (C) is a compound that undergoes a crosslinkingreaction with the hydroxyl groups of the hydroxyl-containing resin (A)and the thermosetting functional groups of the compound (D).

Examples of such curing agents (C) include polyisocyanate compounds,melamine resins, guanamine resins, urea resins, etc.

To obtain a coating film having excellent properties in terms of marresistance, hardness, adhesion, etc., it is preferable to use apolyisocyanate compound alone or in combination with a melamine resin.When a polyisocyanate compound and a melamine resin are used incombination, the polyisocyanate compound/melamine resin weight ratio iswithin the range of about 10/90 to about 90/10 on a solids basis,depending on the desired properties.

The polyisocyanate is a compound having two or more free isocyanategroups per molecule. Examples thereof include aliphatic diisocyanatessuch as hexamethylene diisocyanate, trimethyl hexamethylenediisocyanate, dimer acid diisocyanate, lysine diisocyanate, and thelike; alicyclic diisocyanates such as hydrogenated xylylenediisocyanate, cyclohexylene diisocyanate, methylenebis(cyclohexylisocyanate), isophorone diisocyanate, and the like; aromaticdiisocyanates such as tolylene diisocyanate, phenylene diisocyanate,4,4′-diphenylmethane diisocyanate, xylylene diisocyanate,tetramethylxylylene diisocyanate, naphthalene diisocyanate, and thelike; trivalent or higher organic polyisocyanates such as2-isocyanatoethyl-2,6-diisocyanatocaproate,3-isocyanatomethyl-1,6-hexamethylene diisocyanate,4-isocyanatomethyl-1,8-octamethylene diisocyanate (commonly referred toas triaminononane triisocyanate), and the like; etc.

Other usable polyisocyanate compounds are dimers and trimers of theabove polyisocyanate compounds; prepolymers formed by the urethanationreaction of polyisocyanate compounds with polyhydric alcohols,low-molecular-weight polyester resins, water, etc. under the conditionof an excess of isocyanate groups; and so on.

Blocked polyisocyanate compounds wherein the isocyanate groups of theabove polyisocyanate compounds are blocked by a blocking agent may beused. Examples of blocking agents include phenols, oximes, lactams,alcohols, mercaptans, activated methylene compounds such as diethylmalonate, etc. When a blocked polyisocyanate compound is used, it ispreferably used in combination with a catalyst for the dissociation ofthe blocking agent.

Unblocked polyisocyanate compounds and blocked polyisocyanate compoundsmay be used in combination.

A preferable melamine resin is, for example, obtained by etherifyingmethylol groups in a methylolated melamine with a monoalcohol having 1to 8 carbon atoms. In the etherified melamine resin, all the methylolgroups in the methylolated melamine may be etherified, or they may bepartially etherified with some methylol groups or imino groupsremaining. The melamine resin preferably has about 1 to about 5 triazinerings and a number average molecular weight of about 300 to about 2,000.

Examples of etherified melamine resins include alkyl-etherifiedmelamines such as methyl-etherified melamines, ethyl-etherifiedmelamines, butyl-etherified melamines, etc.

Such etherified melamine resins may be used singly or in combination oftwo or more.

Unsaturated Compound (D)

Compound (D) is at least one unsaturated compound selected from thegroup consisting of radical polymerizable unsaturated monomers, radicalpolymerizable unsaturated group-containing resins, and radicalpolymerizable unsaturated group- and thermosetting functionalgroup-containing resins.

A radical polymerizable unsaturated monomer has one or more radicalpolymerizable unsaturated groups per molecule. Examples of such monomersthat may be used are monofunctional polymerizable monomers having oneradical polymerizable unsaturated group per molecule, bifunctionalpolymerizable monomers having two radical polymerizable unsaturatedgroups per molecule, and polyfunctional polymerizable monomers havingthree or more radical polymerizable unsaturated groups per molecule.Specific examples thereof are given below.

Examples of monofunctional polymerizable monomers include styrene,methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate,2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, cyclohexyl(meth)acrylate, cyclohexenyl (meth)acrylate, 2-hydroxyl (meth)acrylate,hydroxypropyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate,ε-caprolactone-modified tetrahydrofurfuryl (meth)acrylate, phenoxyethyl(meth)acrylate, phenoxy polyethylene glycol (meth)acrylate,dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate,isobornyl (meth)acrylate, benzyl (meth)acrylate, ε-caprolactone-modifiedhydroxyethyl (meth)acrylate, polyethylene glycol mono(meth)acrylate,polypropylene glycol mono(meth)acrylate, 2-hydroxy-3-phenoxypropyl(meth)acrylate, 2-hydroxy-3-butoxypropyl (meth)acrylate, phthalic acidmonohydroxyethyl (meth)acrylate, para-cumylphenol ethyleneoxide-modified (meth)acrylate, N-methylol (meth)acrylamide, N-methylol(meth)acrylamide butyl ether, acryloyl morpholine, dimethylaminoethyl(meth)acrylate, N-vinyl-2-pyrrolidone, etc.

Examples of bifunctional polymerizable monomers include ethylene glycoldi(meth)acrylate, diethylene glycol di(meth)acrylate, polyethyleneglycol di(meth)acrylate, propylene glycol di(meth)acrylate, dipropyleneglycol di(meth)acrylate, polypropylene glycol di(meth)acrylate,neopentyl glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate,1,6-hexanediol di(meth)acrylate, bisphenol-A ethylene oxide-modifieddi(meth)acrylate, bisphenol-A propylene oxide-modified di(meth)acrylate,2-hydroxy-1-acryloxy-3-methacryloxypropane, tricyclodecane dimethanoldi(meth)acrylate, di(meth)acryloyloxyethyl acid phosphate, etc. Usablebifunctional monomers include those monomers that are commerciallyavailable under the trade names of “KAYARAD HX-220”, “KAYARAD HX-620”,“KAYARAD R-604” (di(meth)acrylate monomers; products of Nippon KayakuCo., Ltd.), etc.

Examples of polyfunctional polymerizable monomers having three or moreradical polymerizable unsaturated groups per molecule includetrimethylolpropane tri(meth)acrylate, trimethylolpropane ethyleneoxide-modified tri(meth)acrylate, trimethylolpropane propyleneoxide-modified tri(meth)acrylate, glycerin tri(meth)acrylate, glycerinethylene oxide-modified tri(meth)acrylate, glycerin propyleneoxide-modified tri(meth)acrylate, pentaerythritol tri(meth)acrylate,pentaerythritol tetra(meth)acrylate, isocyanuric acid ethyleneoxide-modified triacrylate, dipentaerythritol hexa(meth)acrylate, etc.

To enhance the curability of the coating composition, mar resistance ofthe cured coating film, etc., it is preferable to use bifunctional orhigher radical polymerizable unsaturated monomers.

Examples of radical polymerizable unsaturated group-containing resinsinclude unsaturated acrylic resins, unsaturated urethane resins,unsaturated epoxy resins, polyester (meth)acrylates, unsaturatedsilicone resins, etc.

A radical polymerizable unsaturated group- and thermosetting functionalgroup-containing resin has one or more radical polymerizable unsaturatedgroups and one or more thermosetting functional groups per molecule. Toimprove the curability of the coating composition, the resin preferablycontains two or more radical polymerizable unsaturated groups and two ormore thermosetting functional groups per molecule. Examples ofthermosetting functional groups include hydroxyl groups, acid groups,epoxy groups, isocyanate groups, and like functional groups. Examples ofacid groups include carboxyl groups, phosphoric acid groups, etc.

Examples of resins containing radical polymerizable unsaturated groupsand thermosetting functional groups include radical polymerizableunsaturated group- and hydroxyl group-containing acrylic resins, radicalpolymerizable unsaturated group- and carboxyl group-containing acrylicresins, radical polymerizable unsaturated group- and epoxygroup-containing acrylic resins, radical polymerizable unsaturatedgroup- and isocyanate group-containing acrylic resins, radicalpolymerizable unsaturated group- and hydroxyl group-containing polyesterresins, radical polymerizable unsaturated group- and carboxylgroup-containing polyester resins, radical polymerizable unsaturatedgroup- and epoxy group-containing cresol novolac epoxy resins, etc.

In the thermosetting and photocurable coating composition (I) of thepresent invention, the proportions of hydroxyl-containing resin (A),copolymer (B), and curing agent (C) may be selected from a wide range.To obtain excellent properties in terms of the curability of the coatingcomposition, mar resistance of the coating film, etc., the coatingcomposition (I) preferably comprises about 20% to about 60% by weight ofhydroxyl-containing resin (A), about 10% to about 45% by weight ofcopolymer (B), and about 5% to about 50% by weight of curing agent (C)based on the total solids weight of hydroxyl-containing resin (A),copolymer (B), and curing agent (C). More preferably, the coatingcomposition (I) comprises about 30% to about 55% by weight ofhydroxyl-containing resin (A), about 20% to about 40% by weight ofcopolymer (B), and about 10% to about 40% by weight of curing agent (C)based on the total solids weight of hydroxyl-containing resin (A),copolymer (B), and curing agent (C).

The proportion of unsaturated compound (D) is preferably in the range ofabout 1 to about 50 parts by weight, and more preferably in the range ofabout 1 to about 30 parts by weight, per 100 parts by weight of thetotal solids content of hydroxyl-containing resin (A), copolymer (B),and curing agent (C). A proportion of unsaturated compound (D) that isgreater than 50 parts by weight is undesirable in that it results inimpaired stability of the coating composition as well as poor adhesionof a coating film.

Thermosetting and Photocurable Coating Composition (II)

Thermosetting and photocurable coating composition (II) comprises: (A) ahydroxyl-containing resin; (C) a curing agent; and (E) a maleimidecompound. Those hydroxyl-containing resins (A) and curing agents (C)that can be used for the above coating compositions (I) can be used forcoating compositions (II).

Maleimide Compound (E)

The maleimide compound (E) is a maleimide group-containing polyetherbismaleimide acetic acid ester compound represented by formula (2):

wherein m is an integer from 1 to 6, n is an integer from 1 to 17, andthe maleimide compound (E) has a number average molecular weight of2,000 or less.

To enhance the curability of the coating composition, hardness of theresulting coating film, etc., the above maleimide compound (E) having anumber average molecular weight of 2,000 or less is used. The maleimidecompound (E) preferably has a number average molecular weight of about500 to about 1,800.

The use of the maleimide compound (E) in the coating composition (II)enables the formation of a cured coating film by ultraviolet irradiationwith little or no photopolymerization initiator added.

When such a maleimide compound (E) is incorporated in, for example,clear coating compositions, and, in particular, top clear coatingcompositions for automobile bodies or automobile body parts, coatingfilm properties such as mar resistance (including resistance to marringby car washes), scratch resistance, gasoline resistance, adhesion, etc.can be improved without impairing the transparency of the resultingcoating film.

For example, “LUMICURE MIA 200” (trade name; product of Dainippon Inkand Chemicals, Inc.; ultraviolet-curable oligomer) may be used asmaleimide compound (E).

In the thermosetting and photocurable coating composition (II) of thepresent invention, the proportions of hydroxyl-containing resin (A) andcuring agent (C) may be selected from a wide range. To obtain excellentproperties in terms of the curability of the coating composition, marresistance of the coating film, etc., the coating composition (II)preferably comprises about 60% to about 90% by weight ofhydroxyl-containing resin (A) and about 10% to about 40% by weight ofcuring agent (C) based on the total solids weight of hydroxyl-containingresin (A) and curing agent (C). More preferably, the coating composition(II) comprises about 70% to about 85% by weight of hydroxyl-containingresin (A) and about 15% to about 30% by weight of curing agent (C) basedon the total solids weight of hydroxyl-containing resin (A) and curingagent (C).

The proportion of maleimide compound (E) is preferably in the range ofabout 1 to about 50 parts by weight, and more preferably in the range ofabout 5 to about 30 parts by weight, per 100 parts by weight of thetotal solids content of hydroxyl-containing resin (A) and curing agent(C). A proportion of maleimide compound (E) that is greater than 50parts by weight is undesirable in that it not only fails to improvecoating film properties such as mar resistance, scratch resistance,gasoline resistance, adhesion, etc., but also impairs the stability ofthe coating composition.

Thermosetting and Photocurable Coating Composition (III)

Thermosetting and photocurable coating composition (III) comprises: (A)a hydroxyl-containing resin; (B) a copolymer; (C) a curing agent; and(E) a maleimide compound. In each component, what can be used for theabove coating compositions (I) and (II) can be used for coatingcomposition (III).

The use of copolymer (B) and maleimide compound (E) in combinationenables the formation of cured coating films with improved filmproperties in mar resistance, scratch resistance, gasoline resistance,adhesion, etc. on a coating line under the conditions of limited lightirradiation amount and limited heating time.

In the thermosetting and photocurable coating composition (III) of thepresent invention, the proportions of hydroxyl-containing resin (A),copolymer (B), and curing agent (C) may be selected from a wide range.To obtain excellent properties in terms of the stability of the coatingcomposition, etc., the coating composition (III) preferably comprisesabout 20% to about 60% by weight of hydroxyl-containing resin (A), about10% to about 45% by weight of copolymer (B), and about 5% to about 50%by weight of curing agent (C) based on the total solids weight ofhydroxyl-containing resin (A), copolymer (B), and curing agent (C). Morepreferably, the coating composition (III) comprises about 30% to about55% by weight of hydroxyl-containing resin (A), about 20% to about 40%by weight of copolymer (B), and about 10% to about 40% by weight ofcuring agent (C) based on the total solids weight of hydroxyl-containingresin (A), copolymer (B), and curing agent (C).

The proportion of maleimide compound (E) is usually in the range ofabout 1 to about 50 parts by weight, and preferably in the range ofabout 10 to about 30 parts by weight, per 100 parts by weight of thetotal solids content of hydroxyl-containing resin (A), copolymer (B),and curing agent (C). A proportion of maleimide compound (E) that isgreater than 50 parts by weight is undesirable in that it not only failsto improve coating film properties such as mar resistance, scratchresistance, gasoline resistance, adhesion, etc., but also impairs thestability of the coating composition.

The above-described thermosetting and photocurable coating compositions(II) and (III) may further comprise at least one unsaturated compound(D) selected from the group consisting of radical polymerizableunsaturated monomers, radical polymerizable unsaturated group-containingresins, and radical polymerizable unsaturated group- and thermosettingfunctional group-containing resins.

When unsaturated compound(s) (D) is incorporated in the thermosettingand photocurable coating compositions (II) and (III), the proportion ofunsaturated compound (D) is preferably in the range of about 1 to about50 parts by weight, and more preferably in the range of about 1 to about30 parts by weight, per 100 parts by weight of the total solids contentof hydroxyl-containing resin (A) and curing agent (C) or per 100 partsby weight of the total solids content of hydroxyl-containing resin (A),copolymer (B), and curing agent (C). A proportion of unsaturatedcompound (D) that is greater than 50 parts by weight is undesirable inthat it results in impaired stability of the coating composition as wellas poor adhesion of a coating film.

Photopolymerization Initiator (F)

The thermosetting and photocurable coating compositions (I) to (III) ofthe present invention may optionally contain a photopolymerizationinitiator (F).

To obtain excellent curability, finish quality, etc., the amount ofphotopolymerization initiator (F) is preferably in the range of about0.1 to about 20 parts by weight per 100 parts by weight of the totalsolids content of hydroxyl-containing resin (A) and curing agent (C) orper 100 parts by weight of the total solids content ofhydroxyl-containing resin (A), copolymer (B), and curing agent (C). Theamount thereof is more preferably in the range of about 0.2 to about 10parts by weight, and even more preferably in the range of about 0.3 toabout 5 parts by weight, per 100 parts by weight of the total solidscontent of hydroxyl-containing resin (A) and curing agent (C) or per 100parts by weight of the total solids content of hydroxyl-containing resin(A), copolymer (B), and curing agent (C).

Examples of photopolymerization initiators include benzoin, benzoinmethyl ether, benzoin ethyl ether, benzoin isobutyl ether,diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropane-1-one, benzyldimethyl ketal, 1-hydroxycyclohexyl-phenylketone,2-methyl-2-morpholino(4-thiomethylphenyl)propane-1-one,2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone,2,4,6-trimethylbenzoylphenylphosphine oxide,bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide,2,4,6-trimethylbenzoylphenylethoxyphosphine oxide, benzophenone, methylo-benzoylbenzoate, hydroxybenzophenone, 2-isopropylthioxanthone,2,4-dimethylthioxanthone, 2,4-diethylthioxanthone;2,4-dichlorothioxanthone, 2,4,6-tris(trichloromethyl)-s-triazine,2-methyl-4,6-bis(trichloro)-s-triazine,2-(4-methoxyphenyl)-4,6-bis(trichloromethyl)-s-triazine, etc.

Such photopolymerization initiators may be used singly or in combinationof two or more.

The photopolymerization initiators may be used in combination withphotosensitizers to accelerate the photopolymerization reaction.Examples of such photosensitizers include tertiary amines such astriethylamine, triethanolamine, methyldiethanolamine, methyl4-dimethylaminobenzoate, ethyl 4-dimethylaminobenzoate, isoamyl4-dimethylaminobenzoate, (2-dimethylamino)ethyl benzoate, Michler'sketone, 4,4′-diethylaminobenzophenone, etc.; alkylphosphines such astriphenylphosphine, etc.; thioethers such as β-thiodiglycol, etc.; andso on.

Light Stabilizer

The thermosetting and photocurable coating composition of the presentinvention may optionally contain a light stabilizer to enhance theweatherability of the coating film. Examples of light stabilizersinclude hindered amine light stabilizers, which function as radicalchain inhibitors to capture active radical species generated in thecourse of deterioration of a coating film. Light stabilizers may be usedin combination with ultraviolet absorbers, which are described later.

Among hindered amine light stabilizers, hindered piperidines arepreferable since they have excellent light stabilization properties.

Examples of hindered piperidines are monomeric hindered piperidines suchas bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate,bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate,bis(N-methyl-2,2,6,6-tetramethyl-4-piperidinyl) sebacate,4-benzoyloxy-2,2′,6,6′-tetramethylpiperidine,bis(1,2,2,6,6-pentamethyl-4-piperidyl){[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl)butylmalonate, etc.; oligomeric hindered piperidines such aspoly{[6-(1,1,3,3-tetramethylbutyl)imino-1,3,5-triazine-2,4-diyl][(2,2,6,6-tetramethyl-4-piperidyl)imino]hexamethylene[(2,2,6,6-tetramethyl-4-piperidyl)iminol]},etc.; polyester hindered piperidines such as polyesters of4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol and succinic acid,etc; and so on.

When a light stabilizer is incorporated in the thermosetting andphotocurable coating composition of the present invention, theproportion of light stabilizer in the solids content of the coatingcomposition is usually in the range of about 0.1% to about 10% byweight.

Ultraviolet Absorber

The coating composition of the present invention may optionally containan ultraviolet absorber to increase the weatherability of a coatingfilm. The ultraviolet absorber absorbs incident light and converts lightenergy into a harmless form like heat energy to inhibit coating filmdeterioration due to light. Ultraviolet absorbers may be used incombination with the above-described light stabilizers.

Known ultraviolet absorbers may be used. Examples thereof includebenzotriazole absorbers, triazine absorbers, salicylic acid derivativeabsorbers, benzophenone absorbers, etc.

Examples of benzotriazole absorbers include2-(2′-hydroxy-5′-methylphenyl)benzotriazole,2-(2′-hydroxy-5′-t-butylphenyl)benzotriazole,2-(2′-hydroxy-3′,5′-di-t-butylphenyl)benzotriazole,2-(2′-hydroxy-3′-t-butyl-5′-methylphenyl)-5-chlorobenzotriazole,2-(2′-hydroxy-3′,5′-di-t-butylphenyl)-5-chlorobenzotriazole,2-(2′-hydroxy-3′,5′-di-t-amylphenyl)benzotriazole,2-(2′-hydroxy-4′-octoxyphenyl)benzotriazole,2-{2′-hydroxy-3′-(3″,4″,5″,6″-tetrahydrophthalimidemethyl)-5′-methylphenyl}benzotriazole,etc.

Examples of triazine absorbers include2,4-bis(2,4-dimethylphenyl)-6-(2-hydroxy-4-isooctyloxyphenyl)-1,3,5-triazine,2-[4((2-hydroxy-3-dodecyloxypropyl)-oxy)-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine,2-[4-((2-hydroxy-3-tridecyloxypropyl)-oxy)-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine,2-(2,4-dihydroxyphenyl)-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, etc.

Examples of salicylic acid derivative absorbers include phenylsalicylate, p-octylphenylsalicylate, 4-tert-butylphenylsalicylate, etc.

Examples of benzophenone absorbers include 4-dihydroxybenzophenone,2-hydroxy-4-methoxybenzophenone, 2,2′-dihydroxy-4-methoxybenzophenone,2-hydroxy-4-methoxy-2′-carboxybenzophenone,2-hydroxy-4-methoxy-5-sulfobenzophenone trihydrate,2,2′-dihydroxy-4,4′-dimethoxybenzophenone,2-hydroxy-4-octoxybenzophenone, 2-hydroxy-4-octadecyloxybenzophenone,sodium 2,2′-dihydroxy-4,4′-dimethoxy-5-sulfobenzophenone,2,2′,4,4′-tetrahydroxybenzophenone, 4-dodecyloxy-2-hydroxybenzophenone,5-chloro-2-hydroxybenzophenone, resorcinol monobenzoate, 2,4-dibenzoylresorcinol, 4,6-dibenzoyl resorcinol, hydroxydodecylbenzophenone,2,2′-dihydroxy-4-(3-methacryloxy-2-hydroxypropoxy)benzophenone, etc.

When an ultraviolet absorber is incorporated in the thermosetting andphotocurable coating composition of the invention, the proportion ofultraviolet absorber in the solids content of the coating composition isusually in the range of about 0.1% to about 10% by weight.

When the coating composition of the present invention is a clear coatingcomposition, it may contain coloring pigment and/or luster pigment tothe extent that the transparency of the resulting coating film is notimpaired. When the coating composition of the invention is a coloredcoating composition, it may contain coloring pigment and/or lusterpigment so as to produce the intended color tone. The coatingcomposition of the invention may optionally contain other pigments suchas extender pigments.

Examples of coloring pigments include inorganic pigments such astitanium dioxide, iron oxides, etc.; organic pigments such asphthalocyanine blue, quinacridone red, perylene red, phthalocyaninegreen, etc.; and so on. Examples of luster pigments include aluminumflakes, mica flakes, etc. Examples of extender pigments include bariumsulfate, calcium carbonate, talc, clay, etc.

If necessary, known additives such as surface modifiers, anti-saggingagents, anti-settling agents, plasticizers, etc. may be added to thecoating composition of the invention.

Because of its excellent coating film surface properties, the coatingcomposition of the present invention is preferably used as a clearcoating composition to form a top clear coat on automobile bodies orautomobile body parts.

Method of Preparing Coating Composition

The thermosetting and photocurable coating composition of the presentinvention can be prepared by mixing the above-described componentsaccording to known methods. When resins are in forms such asorganic-solvent solutions, emulsions, etc., they can be mixed as theyare. When pigments are used, they may be mixed with dispersion resins tobe used in paste form. When mixing components together, organic solvent,water, or a liquid mixture of these may be optionally added to thecomponents.

Examples of organic solvents that may be used in the coating compositionof the present invention include aromatic solvents such as toluene,xylene, etc.; ester solvents such as ethyl acetate, propyl acetate,butyl acetate, methoxybutyl acetate, amyl acetate, methyl cellosolveacetate, cellosolve acetate, diethylene glycol monomethyl ether acetate,carbitol acetate, etc.; ether solvents such as dioxane, ethylene glycoldiethyl ether, ethylene glycol dibutyl ether, etc.; ketone solvents suchas acetone, methyl ethyl ketone, methyl isobutyl ketone, etc.; and soon. Such organic solvents may be used singly or in combination of two ormore.

The coating composition of the present invention may be in the form ofan organic solvent-based coating composition or an aqueous coatingcomposition. The coating composition usually has a solids content ofabout 20% to about 80% by weight.

Method of Forming a Coating Film

The thermosetting and photocurable coating composition of the presentinvention can be suitably used in various methods of forming a coatingfilm on a substrate, as described hereinafter.

Substrate to be Coated

Examples of substrates to be coated include the bodies and body parts ofvehicles such as automobiles, motorcycles, etc. Other examples ofsubstrates to be coated are materials for vehicle body components andthe like, including metal substrates such as aluminum sheets and plates,aluminum alloy sheets and plates, steel sheets and plates such ascold-rolled steel sheets and plates, galvanized steel sheets and plates,zinc alloy-plated steel sheets and plates, stainless steel sheets andplates, tin-plated steel sheets and plates, etc.; various plasticsubstrates; and so on.

Such vehicle bodies, body parts, and metal substrates to be coated mayhave metal surfaces chemically treated by phosphating, chromating, etc.Further, such vehicle bodies, metal substrates, etc. to be coated mayhave an undercoating film, which is formed from electrodepositioncoating compositions, etc., and/or an intermediate coating film.

Methods of Coating and Curing

The coating method using the coating composition of the presentinvention is not limited. A wet coating film can be formed by methodssuch as air spray coating, airless spray coating, rotary atomizationcoating, curtain coating, etc. In air spray coating, airless spraycoating, and rotary atomization coating, an electrostatic charge may beoptionally applied. Of such methods, air spray coating, rotaryatomization coating, etc. are preferable. The coating composition ispreferably applied to a film thickness of about 10 to about 70 μm (whencured).

In air spray coating, airless spray coating, and rotary atomizationcoating, it is preferable to carry out dilution with organic solventand/or water so as to adjust the viscosity of the coating composition toa suitable range for the coating method, the viscosity being usuallywithin the range of about 15 to about 60 seconds at 20° C. (viscometer:Ford cup No. 4).

After coating a substrate with the coating composition, the resultingwet coating film is cured by irradiating with light after heating or byheating after irradiating with light.

Heating can be performed by known heating means. Examples thereofinclude drying furnaces such as hot air furnaces, electric furnaces,infrared heating furnaces, etc.

The heating temperature is usually within the range of about 50° C. toabout 200° C., and preferably within the range of about 70° C. to about160° C. The heating time is usually within the range of about 5 to about30 minutes.

Light irradiation is usually performed using ultraviolet light having awavelength of about 200 to about 450 nm. The light source can besuitably selected to provide wavelengths to which a selectedphotopolymerization initiator is highly sensitive. Examples of sourcesof the above-mentioned ultraviolet light include high pressure mercurylamps, ultrahigh pressure mercury lamps, xenon lamps, carbon arc lamps,metal halide lamps, sunlight, etc.

The coating film is irradiated with ultraviolet light at an intensity ofpreferably about 100 to about 5,000 mJ/cm², and more preferably about300 to about 3,000 mJ/cm². The irradiation time is usually about 3seconds to about 3 minutes.

As described above, the wet coating film can be sufficiently cured byfirst heating and thereafter irradiating with light or by firstirradiating with light and thereafter heating.

Therefore, in the heat-curing step combined with the photocuring step onan automobile body coating line, the coating film can be cured asnecessary by, for example, heating at about 140° C. for about 20minutes. When the conveyor speed is 3 m/min, the required length of adrying furnace line can be reduced to about 60 m, which is about halfthe length usually required. Space and energy thus can be saved.

Steps of Forming a Coating Film

The coating composition of the present invention is capable of forming acoating film having excellent properties in terms of mar resistance,scratch resistance, gasoline resistance, adhesion, etc. Therefore, thecoating composition of the invention is preferably used as a clearcoating composition to form a top clear coat in a method for forming amultilayer coating film on a substrate. In particular, the coatingcomposition of the invention is preferably used as a clear coatingcomposition for automobile bodies or automobile body parts.

The coating film formation method of the present invention comprisesforming one or two colored base coats and then one or two clear coats ona substrate to be coated to form a multilayer coating film, the topclear coat being formed from the coating composition (I), (II), or (III)of the invention.

Especially preferable substrates to be coated by the coating filmformation method of the present invention are automobile bodies orautomobile body parts.

More specifically, the coating film formation method of the presentinvention may be, for example, any of the following multilayer coatingfilm formation methods (a) to (c), wherein the top clear coat is formedfrom the clear coating composition (I), (II), or (III) of the invention.

Method (a): a two-coat method of forming a multilayer coating film,wherein a colored base coat and a top clear coat are formed on asubstrate to be coated.

Method (b): a three-coat method of forming a multilayer coating film,wherein a colored base coat, a clear coat, and a top clear coat areformed in that order on a substrate to be coated.

Method (c): a three-coat method of forming a multilayer coating film,wherein a first colored base coat, a second colored base coat, and a topclear coat are formed in that order on a substrate to be coated.

Moreover, the coating composition of the present invention can also beused when forming a single-layer coating film. In this case, the coatingcomposition may be a clear coating composition or may be a coloredcoating composition. Method (d), which is a film formation method to beused in this case, is described below in addition to the above methods.

Method (d): a one-coat method of forming a coating film, wherein asubstrate is coated with the coating composition of the presentinvention in a single layer, and the coating composition is cured.

The steps of forming a coating film in methods (a), (b), (c), and (d)are described below in detail.

In the above method (a), known colored coating compositions and knownlustrous coating compositions may be used as coating compositions forforming the colored base coat.

The colored base coating composition is an organic solvent-based oraqueous coating composition containing a base resin, crosslinking agent,and coloring pigment and/or luster pigment.

Examples of base resins include acrylic resins, vinyl resins, polyesterresins, alkyd resins, urethane resins, etc.; and at least one base resinis used. The base resin has crosslinkable functional groups such ashydroxyl groups, epoxy groups, carboxyl groups, alkoxysilyl groups, etc.Examples of crosslinking agents include alkyl-etherified melamineresins, urea resins, guanamine resins, polyisocyanate compounds, blockedpolyisocyanate compounds, epoxy compounds, carboxyl-containingcompounds, etc.; and at least one crosslinking agent is used. Theproportions of base resin and crosslinking agent are preferably 50% to90% by weight of base resin and 50% to 10% by weight of crosslinkingagent, based on the total amount of these components.

Examples of coloring pigments and luster pigments are those previouslymentioned as pigments usable for the coating composition of the presentinvention.

In each method, the coating with colored base coating compositions andclear coating compositions may be carried out using coating methods suchas airless spray coating, air spray coating, rotary atomization coating,etc. In these coating methods, an electrostatic charge may be optionallyapplied.

In method (a), the substrate is coated with a colored base coatingcomposition to a film thickness of about 10 to about 50 μm (when cured).After coating, the base coating composition is either cured by heatingat about 100° C. to about 180° C., and preferably at about 120° C. toabout 160° C., for about 10 to about 40 minutes, or is not cured withthe coated substrate being left to stand at room temperature for severalminutes or being preheated at about 40° C. to about 100° C. for about 1to about 20 minutes.

To form a top clear coat, the coated substrate is further coated withthe clear coating composition of the present invention to a filmthickness of about 10 to about 70 μm (when cured). The coated substrateis then either first heated and thereafter irradiated with light, or isfirst irradiated with light and thereafter heated. Thus a curedmultilayer coating film can be formed. Preferably, heating is performedat about 100° C. to about 180° C., particularly at about 120° C. toabout 160° C., for about 5 to about 30 minutes to cure the coating filmby crosslinking. Light irradiation is performed under theabove-described conditions of wavelength, light source, irradiationintensity, and irradiation time.

Hereinafter, the method of applying a base coating composition,thereafter applying a clear coating composition without heat-curing thebase coat, and curing the two coats simultaneously may be referred to asa two-coat one-bake method. The method of applying a base coatingcomposition, heat-curing the base coat, thereafter applying a clearcoating composition, and curing the clear coat may be referred to as atwo-coat two-bake method.

The above-described colored base coating composition for method (a) canbe used as the colored base coating composition for method (b). Anycoating composition for forming a clear coating film can be used as thefirst clear coating composition to form a clear coat. For example,coating compositions that contain little or no pigment used in knowncolored base coating compositions can be used. The coating compositionof the present invention is used as the second clear coating compositionto form a top clear coat. In addition, the clear coating composition ofthe invention may also be used as the first clear coating composition,so that both the clear coat and the top clear coat are formed from theclear coating composition of the invention.

In method (b), as in method (a), a colored base coating composition isapplied to the substrate and either cured by heating, or not cured withthe coated substrate being left to stand at room temperature for severalminutes or being preheated. The colored base coating film is then coatedwith a first clear coating composition to a film thickness of about 10to about 50 μm (when cured). The coating composition is either cured byheating at about 100° C. to about 180° C., and preferably at about 120°C. to about 160° C., for about 10 to about 40 minutes, or is not curedwith the coated substrate being left to stand at room temperature forseveral minutes or being preheated.

The coated substrate is then further coated with the coating compositionof the present invention as a second clear coating composition to acoating film thickness of about 10 to about 50 μm (when cured). Thecoated substrate is then either first heated and thereafter irradiatedwith light, or is first irradiated with light and thereafter heated.Thus a cured multilayer coating film can be formed. The conditions forheating and irradiation are the same as in method (a).

Hereinafter, the method of applying a base coating composition, applyinga first clear coating composition without heat-curing the base coatingcomposition, applying a second clear coating composition without curingthe first clear coating composition, and then curing the three coatssimultaneously may be referred to as a three-coat one-bake method. Themethod of applying a base coating composition, applying a first clearcoating composition without heat-curing the base coating composition,curing these coats simultaneously, and then applying and curing a secondclear coating composition may be referred to as a three-coat two-bakemethod. Moreover, the method of applying and heat-curing a base coatingcomposition, applying and curing a first clear coating composition, andthen applying and curing a second clear coating composition may bereferred to as a three-coat three-bake method.

The above-described colored base coating composition for method (a) canbe used as the first colored base coating composition for method (c).Since the second colored base coating composition is applied onto thecoat of the first colored base coating composition, the second coloredbase coating composition is usually a clear colored composition that hasweak hiding power such that the color tone of the first colored coatingsurface is visible through the second colored base coating film.

Hence, the second colored base coating composition is preferablyprepared by selecting a suitable type of pigment and adjusting theamount thereof in view of the first colored base coating compositionsuch that the hiding power of the second colored base composition isweaker than that of the first colored base composition. The coatingcomposition of the present invention is used as the clear coatingcomposition for the top clear coat.

In method (c), as in method (a), a first colored base coatingcomposition is applied to the substrate and either cured by heating, ornot cured with the coated substrate being left to stand at roomtemperature for several minutes or being preheated. The first coloredbase coating film is then coated with the second colored base coatingcomposition to a film thickness of about 10 to about 50 μm (when cured).The coating composition is either cured by heating at about 100° C. toabout 180° C., and preferably at about 120° C. to about 160° C., forabout 10 to about 40 minutes, or is not cured with the coated substratebeing left to stand at room temperature for several minutes or beingpreheated.

The coated substrate is then further coated with the coating compositionof the invention as a top clear coating composition to a film thicknessof about 10 to about 50 μm (when cured). The coated substrate is theneither first heated and thereafter irradiated with light, or is firstirradiated with light and thereafter heated. Thus a cured multilayercoating film can be formed. The conditions for heating and irradiationare the same as in method (a).

Hereinafter, the method of applying a first base coating composition,applying a second base coating composition without heat-curing the firstbase coating composition, applying a clear coating composition withoutcuring the second base coating composition, and then curing the threecoats simultaneously may be referred to as a three-coat one-bake method.The method of applying and heat-curing a first base coating composition,applying a second base coating composition, applying a clear coatingcomposition without curing the second base coating composition, and thencuring these coats simultaneously may be referred to as a three-coattwo-bake method. Moreover, the method of applying and heat-curing afirst base coating composition, applying and curing a second basecoating composition, and then applying and curing a clear coatingcomposition may be referred to as a three-coat three-bake method.

In method (d), the substrate is coated with the coating composition ofthe present invention to a film thickness of about 10 to about 50 μm(when cured) by the same coating method as in method (a). The coatedsubstrate is either first heated and thereafter irradiated with light,or is first irradiated with light and thereafter heated. Thus a curedsingle-layer coating film can be formed. The conditions for heating andirradiation are the same as in method (a).

EFFECT OF THE INVENTION

The coating composition and the coating film formation method accordingto the present invention achieve the following remarkable effects.

(1) As compared with conventional thermosetting coating compositions,the thermosetting and photocurable coating composition of the presentinvention enables shortening of the time to cure a coating film andreduction of the size of coating facilities, etc., thereby contributingto saving space and energy. The coating composition of the inventionshortens the time for heat-curing, thereby decreasing CO₂, soot, etc.

(2) The coating film after application of the coating composition of thepresent invention can be fully cured by first heating and thereafterirradiating with light or by first irradiating with light and thereafterheating. Therefore, the coating film obtained by the coating filmformation method of the present invention has better film properties interms of mar resistance, scratch resistance, gasoline resistance,adhesion, etc. than a film cured only by irradiating with light.

(3) Therefore, in particular, when the coating composition of thepresent invention is used to form a top clear coat on an automobile bodyor automobile body part, the resulting coating film has remarkablyimproved film properties in terms of mar resistance (includingresistance to marring by car washes), scratch resistance, etc.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is described below in more detail with referenceto Production Examples, Examples, and Comparative Examples. However, thepresent invention is not limited to these examples. In the examples,parts and percentages are expressed on a weight basis.

Production of Hydroxyl-Containing Resin (A)

Production Example 1 Production of Hydroxyl-Containing Polyester Resin(A-1)

“Monomer mixture 1” below was placed into a four-necked flask equippedwith a heater, a stirrer, a thermometer, a reflux condenser, and arectification column, and was heated to 160° C. The contents of theflask were heated from 160° C. to 230° C. over 3 hours, and maintainedat 230° C. for 1 hour. The generated condensation water was distilledoff via the rectification column. The rectification column was replacedwith a water separator, and 5 parts of xylene was added to the contentsof the flask. Xylene and remaining condensation water was refluxed, thusfurther removing water by azeotropy with the xylene.

Two hours after the addition of xylene, acid value measurements werestarted. When the acid value reached 2 mg KOH/g, the mixture was cooledto 140° C. Phthalic anhydride was then added to the mixture, which wasmaintained at 140° C. for 2 hours to perform an addition reaction. Thereaction mixture was thereafter cooled to terminate the reaction. Amixed solvent of xylene/aromatic component-containing high-boilingpetroleum solvent (trade name: “Swasol 1000”, product of Cosmo Oil Co.,Ltd.) (weight ratio: 50/50) was further added, giving polyester resin(A-1) with a solids content of 70%. Polyester resin (A-1) had a weightaverage molecular weight of 28,800 and a hydroxyl value of 157 mg KOH/g.

“Monomer mixture 1”:

1,4-cyclohexanedimethanol 74 parts Trimethylolpropane 65 parts1,4-cyclohexanedicarboxylic acid 66 parts Adipic acid 74 partsDibutyltin dilaurate 0.5 parts 

Production Examples 2 and 3 Production of Hydroxyl-Containing PolyesterResins (A-2) and (A-3)

Except for using monomer components as shown in Table 1, the procedureof Production Example 1 was repeated to obtain polyester resin (A-2) andpolyester resin (A-3), each with a solids content of 70%. Polyesterresin (A-2) had a weight average molecular weight of 32,000 and ahydroxyl value of 150 mg KOH/g. Polyester resin (A-3) had a weightaverage molecular weight of 30,000 and a hydroxyl value of 172 mg KOH/g.

Table 1 shows the monomer components of polyester resins (A-1) to (A-3),and the proportion of alicyclic polybasic acid and/or alicyclicpolyhydric alcohol of the monomers in total.

TABLE 1 Polyester resin No. (A-1) (A-2) (A-3) 1,4-cyclohexanedimethanol74 94 Trimethylolpropane 65 85 65 Neopentyl glycol 531,4-cyclohexanedicarboxylic acid 66 100 Phthalic anhydride 56 Adipicacid 74 74 Dibutyltin dilaurate 0.5 0.5 0.5 Proportion of alicyclicpolybasic acid 50.2 69.0 0 and/or alicyclic polyhydric alcohol of themonomers in total (%)

Production Example 4 Production of Hydroxyl-Containing Acrylic Resin

Four hundred and eighty parts of butyl acetate was placed into areaction vessel equipped with a thermometer, a thermostat, a stirrer, areflux condenser and a dropping funnel, and was heated to 130° C. whilefeeding nitrogen gas into the reaction vessel. While maintaining thesame temperature, a mixed solution of the following monomers andpolymerization initiator was added dropwise over 3 hours via thedropping funnel.

Styrene 200 parts Methyl methacrylate 290 parts Cyclohexyl methacrylate250 parts 2-hydroxyethyl methacrylate 260 parts2,2′-azobis(2-methylbutyronitrile)  50 parts

After completion of the dropwise addition, the mixture was aged at 130°C. for 1 hour, giving a solution of hydroxyl-containing acrylic resinwith a resin solids content of 70%. The obtained resin was analyzed byGPC (gel permeation chromatography) with the result that it had a numberaverage molecular weight of about 8,000. The resin had a hydroxyl valueof 107 mg KOH/g.

Production of Maleimide Group-Containing Copolymer (B)

Production Example 5 Production of Copolymer (B-1)

One thousand parts of butyl acetate was placed into a reaction vesselequipped with a thermometer, a thermostat, a stirrer, a reflux condenserand a dropping funnel, and was heated to 120° C. while feeding nitrogengas into the reaction vessel. While maintaining the same temperature, amixed solution of the following monomers and polymerization initiatorwas added dropwise over 3 hours via the dropping funnel.

Styrene 200 parts Methyl methacrylate 290 parts 2-hydroxyethylmethacrylate 260 parts 2,2′-azobis(2-methylbutyronitrile)  30 partsMaleimide group-containing copolymer (a) 250 parts represented by theformula below

After completion of the dropwise addition, the mixture was aged at 120°C. for 1 hour, giving a maleimide group-containing copolymer (B-1)solution with a resin solids content of 50%. The obtained copolymer wasanalyzed by GPC (gel permeation chromatography) with the result that ithad a number average molecular weight of about 9,000. The copolymer hada hydroxyl value of 107 mg KOH/g.

Production of Clear Coating Composition for Automobile Bodies orAutomobile Body Parts

Example 1

Forty parts of polyester resin (A-1) obtained in Production Example 1,10 parts of polyester resin (A-2) obtained in Production Example 2, 20parts of copolymer (B-1) obtained in Production Example 5, 30 parts ofcuring agent I (Note 1), 15 parts of maleimide compound (Note 2), and 5parts of pentaerythritol triacrylate were mixed with stirring. After 1.5parts of photopolymerization initiator I (Note 3) and 0.5 parts ofphotopolymerization initiator II (Note 4) were added and dissolved inthe mixture, 1 part of ultraviolet absorber (Note 5) and 1 part of lightstabilizer (Note 6) were further added and dissolved in the mixture. Theresulting mixture was diluted with xylene to adjust its viscosity to 25seconds at 20° C. (viscometer: Ford cup No. 4), giving clear coatingcomposition No. 1 for automobile bodies or automobile body parts(hereinafter referred to as “for automobiles”).

The above (Note 1) to (Note 6) indicate the following:

(Note 1) curing agent I: trade name “Sumidur N-3300”, product of SumikaBayer Urethane Co., Ltd., isocyanurate-modified hexamethylenediisocyanate, solids content: 100%

(Note 2) maleimide compound: trade name “LUMICURE MIA 200”, product ofDainippon Ink and Chemicals, Inc., maleimide group-containingultraviolet-curable oligomer

(Note 3) photopolymerization initiator I: trade name “IRGACURE 184”,product of Ciba Specialty Chemicals K.K.,1-hydroxy-cyclohexyl-phenyl-ketone

(Note 4) photopolymerization initiator II: trade name “IRGACURE 819”,product of Ciba Specialty Chemicals K.K.,bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide

(Note 5) ultraviolet absorber: trade name “TINUVIN 400”, product of CibaSpecialty Chemicals K.K., triazine ultraviolet absorber

(Note 6) light stabilizer: trade name “SANOL LS-292”, product of SankyoCo., Ltd., bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate

Examples 2 to 7

Except for using components as shown in Table 2, the procedure ofExample 1 was repeated to obtain clear coating compositions No. 2 to No.7 for automobiles.

TABLE 2 Example 1 2 3 4 5 6 7 Clear coating No. 1 No. 2 No. 3 No. 4 No.5 No. 6 No. 7 composition for automobiles Polyester resin 40 30 30 70(A-1) Polyester resin 10 15 10 70 (A-2) Polyester resin 30 (A-3) Acrylicresin of 40 Production Ex. 4 Copolymer 20 25 30 40 30 (B-1) Curing agentI 30 25 25 30 30 25 25 (Note 1) Curing agent II 5 (Note 7) Curing agentIII 5 5 5 (Note 8) Pentaerythritol 5 10 triacrylate Dipentaerythritol 15hexaacrylate Maleimide compound 15 20 25 25 25 30 (Note 2)Photopolymerization 1.5 1 2 1 0.5 1 1 initiator I (Note 3)Photopolymerization 0.5 0.5 0.5 1 0.5 0.5 0.5 initiator II (Note 4)Ultraviolet absorber 1 0.5 1.5 1 1 0.5 0.5 (Note 5) Light stabilizer 11.5 0.5 1 1 1 1 (Note 6)

Comparative Examples 1 to 4

Except for using components as shown in Table 3, the procedure ofExample 1 was repeated to obtain comparative clear coating compositionsNo. 8 to No. 11 for automobiles.

TABLE 3 Comparative Example 1 2 3 4 Clear coating composition No. 8 No.9 No. 10 No. 11 for automobiles Polyester resin (A-1) Polyester resin(A-2) Polyester resin 70 (A-3) Acrylic resin of 70 70 Production Ex. 4Copolymer (B-1) Curing agent I 30 25 (Note 1) Curing agent II 30 (Note7) Curing agent III 5 (Note 8) Pentaerythritol 30 60 triacrylateDipentaerythritol 20 hexaacrylate Maleimide compound 40 (Note 2)Photopolymerization 2 2 2 initiator I (Note 3) Photopolymerization 0.50.5 0.5 initiator II (Note 4) Ultraviolet absorber 1 1 1 1 (Note 5)Light stabilizer 1 1 1 1 (Note 6)

Tables 2 and 3 show the amounts (parts) of the components of the coatingcompositions on a solids basis. The acrylic resin in Production Example4 corresponds to “hydroxyl-containing resin (A)”; and pentaerythritoltriacrylate and dipentaerythritol hexaacrylate correspond to“unsaturated compound (D)”.

In Tables 2 and 3, (Note 1) to (Note 6) are as indicated above. (Note 7)and (Note 8) indicate the following:

(Note 7) curing agent II: trade name “Cymel 235”, product of MitsuiCytec Ltd., methylated/butylated melamine resin

(Note 8) curing agent III: trade name “Cymel 325”, product of MitsuiCytec Ltd., methylated/imino melamine resin

Production Example 6 Production of Substrate to be Coated

A zinc phosphate-treated galvanized steel sheet (25 cm×25 cm×0.8 mm) wascoated with a cationic electrodeposition coating composition (tradename: “Elecron GT-10LF”, product of Kansai Paint Co., Ltd.) byelectrodeposition to a film thickness of about 20 μm (when cured). Thecoated sheet was heated at 170° C. for 20 minutes to cure the coatingfilm. The sheet was further coated with a coating composition for anautomobile intermediate coat (trade name: “Amilac TP-65-2”, product ofKansai Paint Co., Ltd.) by air spraying to a film thickness of about 35μm (when cured). The coated sheet was heated at 140° C. for 30 minutesto cure the coating film, thus giving a substrate to be coated.

Coating Film Formation Method

Example 8

The substrate to be coated obtained in Production Example 6 was coatedwith an aqueous colored base coating composition (trade name: “WBC-710T(black)”, product of Kansai Paint Co., Ltd., acrylic resin/melamineresin thermosetting coating composition) by air spraying to a filmthickness of about 15 μm (when cured) and was dried at 80° C. for 10minutes to evaporate water in the coating film. The resulting uncuredcoating surface was coated with a clear coating composition (trade name:“Magicron TC-69”, product of Kansai Paint Co., Ltd., acrylicresin/melamine resin thermosetting coating composition) by air sprayingto a film thickness of about 35 μm (when cured). The coated substratewas heated at 140° C. for 30 minutes to simultaneously cure the basecoating film and the clear coating film.

The cured clear coating film was coated with clear coating compositionNo. 1 for automobiles obtained in Example 1 by air spraying to a filmthickness of about 40 μm (when cured). The resulting coating film wasdried at 90° C. for 3 minutes as a preheating step to evaporate solvent.

Subsequently, using a metal halide lamp (output: 120 W/cm), the coatingfilm was irradiated with ultraviolet light (wavelength: about 365 nm)for about 10 seconds at an intensity of 1,000 mJ/cm² for photocuring,and thereafter heated at 140° C. for 5 minutes, thereby being cured.

Thus a multilayer coating film was formed by the three-coat two-bakemethod.

Example 9

A multilayer coating film was formed by the three-coat two-bake methodin the same manner as in Example 8 except that clear coating compositionNo. 2 for automobiles obtained in Example 2 was used in place of clearcoating composition No. 1 for automobiles, and that the coating filmafter photocuring was heated at 140° C. for 10 minutes.

Example 10

A multilayer coating film was formed by the three-coat two-bake methodin the same manner as in Example 9 except that clear coating compositionNo. 3 for automobiles obtained in Example 3 was used in place of clearcoating composition No. 2 for automobiles.

Example 11

A multilayer coating film was formed by the three-coat two-bake methodin the same manner as in Example 8 except that clear coating compositionNo. 4 for automobiles obtained in Example 4 was used in place of clearcoating composition No. 1 for automobiles.

Example 12

A multilayer coating film was formed by the three-coat two-bake methodin the same manner as in Example 8 except that clear coating compositionNo. 5 for automobiles obtained in Example 5 was used in place of clearcoating composition No. 1 for automobiles.

Example 13

A multilayer coating film was formed by the three-coat two-bake methodin the same manner as in Example 8 except that clear coating compositionNo. 6 for automobiles was used in place of clear coating composition No.2 for automobiles.

Example 14

A multilayer coating film was formed by the three-coat two-bake methodin the same manner as in Example 8 except that clear coating compositionNo. 7 for automobiles was used in place of clear coating composition No.2 for automobiles.

Example 15

The substrate to be coated obtained in Production Example 6 was coatedwith an aqueous colored base coating composition (trade name: “WBC-710T(black)”, product of Kansai Paint Co., Ltd., acrylic resin/melamineresin thermosetting coating composition) by air spraying to a filmthickness of about 15 μm (when cured) and was dried at 80° C. for 10minutes to evaporate water in the coating film. The resulting uncuredcoating surface was coated with a clear coating composition (trade name:“Magicron TC-69”, product of Kansai Paint Co., Ltd., acrylicresin/melamine resin thermosetting coating composition) by air sprayingto a film thickness of about 35 μm (when cured).

The uncured clear coating film was coated with clear coating compositionNo. 1 for automobiles obtained in Example 1 by air spraying to a filmthickness of about 40 μm (when cured); The coated substrate was heatedat 140° C. for 30 minutes to cure the colored base coating film and thefirst clear coating film and semicure the top clear coating film.Subsequently, using a metal halide lamp (output: 120 W/cm), the topclear coating film was sufficiently cured by irradiation withultraviolet light (wavelength: about 365 nm) for about 10 seconds at anintensity of 1,000 mJ/cm².

Thus a multilayer coating film was formed by the three-coat one-bakemethod.

Example 16

The substrate to be coated obtained in Production Example 6 was coatedwith an aqueous colored base coating composition (trade name: “WBC-710T(black)”, product of Kansai Paint Co., Ltd., acrylic resin/melamineresin thermosetting coating composition) by air spraying to a filmthickness of about 15 μm (when cured) and was dried at 80° C. for 10minutes to evaporate water in the coating film. The resulting uncuredcoating surface was coated with clear coating composition No. 1 forautomobiles obtained in Example 1 by air spraying to a film thickness ofabout 40 μm (when cured). The resulting coating film was dried at 90° C.for 3 minutes as a preheating step to evaporate solvent.

Subsequently, using a metal halide lamp (output: 120 W/cm), the coatingfilm was irradiated with ultraviolet light (wavelength: about 365 nm)for about 10 seconds at an intensity of 1,000 mJ/cm² for photocuring,and thereafter heated at 140° C. for 30 minutes to simultaneously curethe two coats. Thus a multilayer coating film was formed by the two-coatone-bake method.

Table 4 shows the top-coat clear coating compositions for automobiles,coating film formation steps, and film-curing conditions used in thecoating film formation methods of Examples 8 to 16.

TABLE 4 Example 8 9 10 11 12 13 14 15 16 Clear coating No. 1 No. 2 No. 3No. 4 No. 5 No. 6 No. 7 No. 1 No. 1 composition for automobiles Coatingfilm 3C2B 3C2B 3C2B 3C2B 3C2B 3C2B 3C2B 3C1B 2C1B formation stepsIrradiation Intensity 1000 1000 1000 1000 1000 1000 1000 — 1000 (mJ/cm²)Time 10 10 10 10 10 10 10 — 10 (sec) Heating Temperature 140 140 140 140140 140 140 140 140 (° C.) Time 5 10 10 5 5 10 10 30 30 (min)Irradiation Intensity — — — — — — — 1000 — (mJ/cm²) Time — — — — — — —10 — (sec)

In Table 4, 3C2B, 3C1B, and 2C1B mean three-coat two-bake method,three-coat one-bake method, and two-coat one-bake method, respectively.

Comparative Example 5

A multilayer coating film was formed by the three-coat two-bake methodin the same manner as in Example 8 except that clear coating compositionNo. 8 for automobiles obtained in Comparative Example 1 was used inplace of clear coating composition No. 1 for automobiles.

Comparative Example 6

A multilayer coating film was formed by the three-coat two-bake methodin the same manner as in Example 9 except that clear coating compositionNo. 9 for automobiles obtained in Comparative Example 2 was used inplace of clear coating composition No. 2 for automobiles.

Comparative Example 7

The substrate to be coated obtained in Production Example 6 was coatedwith an aqueous colored base coating composition (trade name: “WBC-710T(black)”, product of Kansai Paint Co., Ltd., acrylic resin/melamineresin thermosetting coating composition) to a film thickness of about 15μm (when cured) and was dried at 80° C. for 10 minutes to evaporatewater in the coating film. The resulting uncured coating surface wascoated with a clear coating composition (trade name: “Magicron TC-69”,product of Kansai Paint Co., Ltd., acrylic resin/melamine resinthermosetting coating composition) to a film thickness of about 35 μm(when cured). The coated substrate was heated at 140° C. for 30 minutesto simultaneously cure the base coating film and the clear coating film.

The cured clear coating film was coated with clear coating compositionNo. 10 for automobiles obtained in Comparative Example 3 by air sprayingto a film thickness of about 40 μm (when cured). The resulting coatingfilm was cured only by heating at 140° C. for 5 minutes, withoutultraviolet irradiation. Thus a multilayer coating film was formed by athree-coat two-bake method.

Comparative Example 8

The substrate to be coated obtained in Production Example 6 was coatedwith an aqueous colored base coating composition (trade name: “WBC-710T(black)”, product of Kansai Paint Co., Ltd., acrylic resin/melamineresin thermosetting coating composition) to a film thickness of about 15μm (when cured) and was dried at 80° C. for 10 minutes to evaporatewater in the coating film. The resulting uncured coating surface wascoated with a clear coating composition (trade name: “Magicron TC-69”,product of Kansai Paint Co., Ltd., acrylic resin/melamine resinthermosetting coating composition) to a film thickness of about 35 μm(when cured). The coated substrate was heated at 140° C. for 30 minutesto simultaneously cure the base coating film and the clear coating film.

The cured clear coating film was coated with clear coating compositionNo. 11 for automobiles obtained in Comparative Example 4 by air sprayingto a film thickness of about 40 μm (when cured). The resulting coatingfilm was dried at 90° C. for 3 minutes as a preheating step to evaporatesolvent. Subsequently, using a 120 W/cm metal halide lamp, the coatingfilm was irradiated with ultraviolet light (wavelength: about 365 nm)for about 10 seconds at an intensity of 1,000 mJ/cm² to photocure thecoating film. Thus a multilayer coating film was formed by a three-coattwo-bake method.

Comparative Example 9

The substrate to be coated obtained in Production Example 6 was coatedwith an aqueous colored base coating composition (trade name: “WBC-710T(black)”, product of Kansai Paint Co., Ltd., acrylic resin/melamineresin thermosetting coating composition) to a film thickness of about 15μm (when cured) and was dried at 80° C. for 10 minutes to evaporatewater in the coating film.

The resulting uncured coating surface was coated with clear coatingcomposition No. 10 for automobiles obtained in Comparative Example 3 byair spraying to a film thickness of about 40 μm (when cured). Theresulting coating film was cured only by heating at 140° C. for 30minutes, without ultraviolet irradiation. Thus a multilayer coating filmwas formed by a two-coat one-bake method.

Table 5 shows the top-coat clear coating compositions for automobiles,coating film formation steps, and film-curing conditions used in thecoating film formation methods of Comparative Examples 5 to 9.

TABLE 5 Comparative Example 5 6 7 8 9 Clear coating No. 8 No. 9 No. 10No. 11 No. 10 composition for automobiles Coating film 3C2B 3C2B 3C2B3C2B 2C1B formation steps Irradiation Intensity 1000 1000 — 1000 —(mJ/cm²) Time 10 10 — 10 — (sec) Heating Temperature 140 140 140 — 140(° C.) Time 5 10 5 — 30 (min)

In Table 5, 3C2B and 2C1B mean three-coat two-bake method and two-coatone-bake method, respectively.

The coated substrates of Examples 8 to 16 and Comparative Examples 5 to9 were each tested for the properties of the coating films formedthereon, as follows.

Degree of curing of coating film: The coating surface was wiped for 50reciprocating strokes with a gauze soaked with xylene and was observedwith the naked eye to evaluate the degree of curing of the coating filmaccording to the following criteria:

-   -   A: No changes occurred on the coating surface. The curing of the        coating film was sufficient.    -   B: The coating surface was marred. The curing of the coating        film was insufficient.    -   C: The coating surface was dissolved by the xylene. The curing        of the coating film was extremely insufficient.

Gasoline resistance: After the coated substrate was immersed in regulargasoline at room temperature for 2 hours, the coating surface wasobserved with the naked eye to evaluate the gasoline resistance of thecoating film according to the following criteria:

-   -   A: There was no blistering or blushing on the coating surface.        The coating film had excellent gasoline resistance.    -   B: There was a little blistering or blushing on the coating        surface. The coating film had somewhat poor gasoline resistance.    -   C: There was considerable blistering or blushing on the coating        surface. The coating film had poor gasoline resistance.

Mar resistance: Polishing sand (trade name: “Daruma cleanser”, productof Yamasan-shouten Ltd.) mixed with an equal weight of water was placedon the coated substrate. While being pressed with the flannel-coveredtester terminal of a friction tester (product of Suga Test InstrumentsCo., Ltd., model: FR-2S), the coated substrate was rubbed back and forthfor 50 reciprocating strokes under a load of 0.5 kg. The coating surfacewas observed with the naked eye to evaluate the mar resistance of thecoating film according to the following criteria:

-   -   A: Little change occurred in the gloss of the coating surface.        The coating film had excellent mar resistance.    -   B. A slight change occurred in the gloss of the coating surface,        but to the extent that was allowable for a product.    -   C: The gloss of the coating surface was impaired. The coating        film had poor mar resistance.    -   C: The gloss of the coating surface was severely impaired. The        coating film had very poor mar resistance.

Scratch length: A continuous load-type scratch strength tester (tradename: “Tribogear type 18L”, product of Shinto Scientific Co., Ltd.) wasused to scratch the coating film of the coated substrate by pulling ascratch needle (made of sapphire, 0.1 mmR) for a distance of 10 cm at aspeed of 30 μm/min under a continuous load of 0 g to 100 g. The length(cm) of the scratch left on the coating film 24 hours after the test wasmeasured.

Knoop hardness: After the coated substrate was left in a thermostaticroom at 20° C. for 4 hours, measurement was conducted using a Tukonhardness tester (TUKON microhardness tester, product of American Chain &Cable Company).

Adhesion: After the coated substrate was immersed in warm water at 40°C. for 240 hours, the cured coating film was given crosscuts with acutter reaching down to the substrate so as to form a grid of 100squares (2 mm×2 mm). Adhesive tape was applied to the surface of thegrid portion and forcefully pulled upward. Peeling of the top clearcoating film was inspected, counting the number of remaining crosscutsquares. A larger number of remaining crosscut squares indicates betteradhesion.

The test results are shown in Table 6.

TABLE 6 Example 8 9 10 11 12 13 14 15 16 Degree of curing A A A A A A AA A Gasoline resistance A A A A A A A A A Mar resistance A A A A A B B AA Scratch length 2 3 2 3 3 3 3 2 2 Knoop hardness 9 8 11 7 7 7 8 9 10Adhesion 100 100 100 100 100 100 100 100 100 Comparative Example 5 6 7 89 Degree of curing A A C A A Gasoline resistance A B C A A Marresistance B B D A C Scratch length 5 6 9 0 7 Knoop hardness 9 5 8 20 8Adhesion 80 100 0 0 100

Table 6 shows that the multilayer coating films obtained in Examples 8to 16 were sufficiently cured and had excellent properties in terms ofgasoline resistance, mar resistance, scratch resistance, Knoop hardness,and adhesion.

1-16. (canceled) 17: A thermosetting and photocurable coating composition comprising: (A) a hydroxyl-containing resin; (B) a maleimide group-containing copolymer obtained by radical copolymerization of a maleimide group-containing monomer (a) with at least one other monomer; (c) a curing agent; and (E) a maleimide compound represented by formula (2):

wherein m is an integer from 1 to 6, n is an integer from 1 to 17, and the maleimide compound (E) has a number average molecular weight of 2,000 or less. 18: A coating composition according to claim 17, wherein the hydroxyl-containing resin (A) is a hydroxyl-containing polyester resin produced by esterifying a polybasic acid (b) with a polyhydric alcohol (c), wherein an alicyclic polybasic acid (b1) and/or an alicyclic polyhydric alcohol (c1) are included in a proportion of 20% or more by weight based on the total weight of polybasic acid (b) and polyhydric alcohol (c). 19: A coating composition according to claim 17, wherein the maleimide group-containing monomer (a) of the copolymer (B) is a tetrahydrophthalmaleimide (meth)acrylate represented by formula (1):

wherein R represents hydrogen atom or methyl group. 20: A coating composition according to claim 17, wherein the curing agent (C) is a polyisocyanate compound. 21: A coating composition according to claim 17, wherein the curing agent (C) is a combination of a polyisocyanate compound and a melamine resin. 22: A coating composition according to claim 17, comprising 20% to 60% by weight of hydroxyl-containing resin (A), 10% to 45% by weight of copolymer (B), and 5% to 50% by weight of curing agent (C) based on the total weight of hydroxyl-containing resin (A), copolymer (B), and curing agent (C); and comprising 1 to 50 parts by weight of maleimide compound (E) per 100 parts by weight of the total of hydroxyl-containing resin (A), copolymer (B), and curing agent (C). 23: A coating composition according to claim 17, further comprising, per 100 parts by weight of the total of hydroxyl-containing resin (A), copolymer (B), and curing agent (C), 1 to 50 parts by weight of at least one unsaturated compound (D) selected from the group consisting of radical polymerizable unsaturated monomers, radical polymerizable unsaturated group-containing resins, and radical polymerizable unsaturated group- and thermosetting functional group-containing resins. 24: A coating composition according to claim 17, further comprising 0.1 to 20 parts by weight of photopolymerization initiator (F) per 100 parts by weight of the total of hydroxyl-containing resin (A), copolymer (B), and curing agent (C). 25: A coating composition according to claim 17, wherein the coating composition is a clear coating composition for automobile bodies or automobile body parts. 26-43. (canceled) 